The purpose of this review is to provide a comprehensive update on the genetic causes of frontotemporal lobar degeneration (FTLD). Approximately 40% to 50% of patients diagnosed with FTLD have a family history of a ''related disorder,'' whereas 10% to 40% have an autosomal dominant family history for the disease. At this time, mutations occurring in 2 independent genes located on the same chromosome (MAPT and GRN) have been shown to cause the majority of cases of autosomal dominant FTLD. Specific genetic, molecular, pathological, and phenotypic variations associated with each of these gene mutations are discussed, as well as markers that may help differentiate the 2. In addition, 3 relatively rare, additional genes known to cause familial FTLD are examined in brief. Lastly, genetic counseling issues which may be important to the community clinician are discussed.